The use of so-called “top drives” in connection with the drilling of boreholes for the purposes of hydrocarbon exploration and production has become commonplace in the industry. In particular, “top drive” drilling operations are recognized by those of ordinary skill in the art as avoiding certain disadvantages of prior art drilling methods. Most notably, “top drive” drilling rigs can avoid the laborious and inefficient use of a “stabber,” a manually controlled apparatus for threadably coupling the downward end of a tubular segment with the upper end of a tubular string extending downwardly into a borehole.
In a typical embodiment, a top drive operation involves the use of a manipulator designed to engage a tubular segment and raise the segment up into a power-assist top-drive apparatus. Specifically, a top end of the tubular segment is engaged by the top drive. The bottom end of the tubular segment engaged by the top drive may then be brought into contact with the top of a tubular string extending into a borehole, and the tubular segment is then threadably rotated into engagement with the tubular string as it is rotated by the top drive.
FIG. 21 shows a typical drilling rig 10 incorporating a top drive drilling system. In particular, rig 10 comprises a frame 12 and a pair of rails 14 along which a top drive assembly generally designated 16 rides for vertical movement thereof. A typical top drive assembly 16 comprises a drive motor 18 and a top drive output shaft 20 extending downwardly from the drive motor 18. The rig defines a drill floor 22 having a central opening 24 through which tubular elements are inserted downwardly into a well hole 26.
Also shown in FIG. 21 is a tubular running apparatus 30 which is adapted to engage the upper end of a tubular segment 32 and to mechanically couple the upper end to the top drive output shaft 20 thereby permitting rotation of the tubular segment 32 under control of the top drive.
The arrangement depicted in FIG. 21 is exemplary of the majority of top-drive drilling systems presently known and used, and such systems are familiar to anyone of ordinary skill in the art. Many variations among particular implementations of top-drive drilling systems have been and will continue to be implemented, and those of ordinary skill in the art having the benefit of the present disclosure will readily comprehend how the present invention may be implemented and deployed in any particular top-drive drilling system.